I'm no flooring contractor or expert, but can offer the fllwg general observations:
(We also assume you have a huge basement!)
Begin as in any other wood floor over slab on or below grade: a vapor barrier and sleepers, either nailed or set in mastic, spanned according to the intended load & local code. PT sleepers are a good idea over subgrade concrete. Lay plywood subfloor as for other flooring.
Over the plywood are placed elastomer blocks, frequently 12" OC, then the MDO, then the maple flooring. A local installer of gym flooring may help you select and procure the correct durometer and spacing of rubber blocks.
IMHO doing this right is not cheap, and if you don't understand the materials or have experience building hardwood floors, you may be better off to hire an experienced installer. Installing maple flooring below grade, even with vapor barrier, may/may not also be a dicey proposition, depending upon your individual site & seasonal moisture conditions. I'd suggest seeking professional advice on-site, to avoid incurring future heartache, before commencing. In any case, it is wise to have all of the flooring stored for a few weeks in the same space prior installation, for it to acclimate to prevailing humidity. There are also other important "tricks of the trade" regarding proper laying & fastening of of the materials, to insure future stability and no buckling.
FWIW, as a former realtor, I doubt one would profit or recoup such an investment on sale of a residence. IMHO it would have to be justified for the present owner's convenience or whim - unless zoning permits use as a studio or like business.
After you correctly design, purchase and build such a floor, you may come to appreciate how your local ballroom can afford let you in the door so cheaply (smile).
